xltronic.com broadcast from the home of Autechre
occasionally has live streams directly from artists themselves. This very, very long set was made by Autechre and streamed via xltronic.com. This is the highest bit-rate version I am aware of. Since streaming is usually done in low resolution, this is likely the best it's going to sound unless Autechre release the source.
160kbps version is the upload, other files were sourced from these.
For free electronic music, check out Karakasa Music!